The invention relates to a method for the identification of the intensity distribution of particle beam pulses generated in a particle beam measuring instrument having a beam blanking system.
The functioning of integrated circuits is usually automatically monitored with computer-controlled test installations. In most cases, however, the tests executed in such fashion are incomplete since perceived faults can only be localized with great difficulty. Particularly during the development phase, additional measurements in the inside of the integrated circuits must therefore be carried out. Electron beam measuring instruments operating in non-contacting and non-destructive fashion are particularly suitable for these purposes, these being increasingly employed in all areas of development and fabrication of micro-electronic components. The electron beam measuring methods most frequently employed in practice are described, for example, in the periodical "Scanning", Vol. 5, (1983) in the survey articles by H. P. Feuerbaum or Menzel and Kubalek on pages 14 through 24 and 103 through 122, both incorporated herein by reference. Particularly illuminating references regarding the localization of faults in LSI circuits are obtained by means of quantitative measurements of the chronological curve of potential at selected nodes of the components to be tested. The primary electron beam generated in the electron-optical column of a modified scanning electron microscope is thereby positioned, for example, to a measuring point. The dislocation of the energy distribution of the secondary electrons triggered at the measuring point which is dependent on the potential of the component is determined in a spectrometer. Quantitative measurements of the curve of potential having a chronological resolution in the nano second range are only possible stroboscopically based on the sampling principle. Given this method from electrical measuring technology, the primary electron beam is pulsed synchronously with the frequency of the signal to be measured and the curve of potential is continuously scanned or sampled by displacing the cut-in time of the primary electron pulses. Undisturbed measurements of the chronological curve of potential can only be implemented when the shape of a technologically unrealizable dirac pulse can be assumed for the primary electron pulse.
Since the beginning of the employment of stroboscopy or the sampling method for measuring the chronological curve of potential in micro-electronic components, the exact identification of the electron pulse duration was an extreme problem. It was thus attempted to derive the pulse duration given a known pulse repetition rate from the reduction of the mean beam current given a pulsed mode of the electron beam measuring instrument in comparison to the beam current given continuous operation. This method, however, only supplies extremely rough estimated values since assumptions regarding the intensity distribution of the primary electron pulses which are not experimentally testable enter into the calculations.
A method for the direct measurement of the primary electron pulse durations in an electron beam measuring instrument is set forth in the dissertation of E. Menzel "Elektronenstrahltestsystem fuer die Funktionskontrolle und Fehleranalyse Hoechstintegrierter Schaltkreise", Universitaet-Gesamthochschule-Duisburg (1981), incorporated herein by reference. The basis of this known method is the transformation of the chronological intensity distribution of the primary electron pulses into a topical distribution which is then sensed or sampled with a topically resolving documentation system. An arrangement for the implementation of this method is essentially formed of a beam blanking system additionally situated in the specimen chamber of an electron beam measuring instrument, said beam blanking system having a separate deflection capacitor, a fine needle point, and an involved control and signal processing electronics. The primary electron pulses generated with the blanking system traverse the linearly rising field of the deflection capacitor, whereby the electrons forming the pulse are deflected to differing degrees in the field of the deflection capacitor in accordance with their chronological arrival. With the assistance of the fine needle point, then, a narrow region of the topical intensity distribution generated in such fashion from the chronological intensity distribution of the primary electron pulse is blanked out, since only primary electrons impinging in the region of the needle tip contribute to the secondary electron signal. The registration of the intensity distribution then occurs by variation of the delay time between the voltage adjacent to the beam blanking system and the voltage of the deflection capacitor.
This known method for direct measurement of the intensity distribution of a primary electron pulse requires a relatively great expense for apparatus and is therefore hardly suited for employment in one of the modified scanning electron microscopes which are predominantly utilized in the framework of electron beam measuring technology.